Paint USED to have a rudimentary, hard-to-use transparency function where you would assign transparency to a certain color.

I was also going to mention this; you can still do it, I bet.. good luck figurign out how, though.. hah!

I tested this with three different versions of windows: 98, 2000, XP

XP had no obvious capability, not even in the Attributes dialogue.

2000 had the option in the Attributes dialogue but it was greyed out, even when attempting to edit a GIF.

98 had the option and it also worked surprisingly enough. I suspect that it might have something to do with having Office 97 installed, whereas neither 2000 or XP had any version of MS Office installed.

interestingly, ctrl+clicking on the color palette will choose the transparent color in all versions, but will only really work in the Win98 version.